Chris Jones, from the UK Met Office Hadley Centre, presented a paper at EGU 2009 yesterday on The Trillionth Tonne. The analysis shows that the key driver of temperature change is the total cumulative amount of carbon emissions. To keep below the 2°C global average temperature rise generally regarded as the threshold for preventing dangerous warming, we need to keep total cumulative emissions below a trillion tonnes. And the world is already halfway there.

Which is why the latest news about Canada’s carbon emissions are so embarrassing. Canada is now top among the G8 nations for emissions growth. Let’s look at the numbers: 747 megatonnes in 2007, up from 592 megatonnes in 1990. Using the figures in the Environment Canada report, I calculated the Canada has emitted over 12 gigatonnes since 1990. That’s 12 billion tonnes. So, in 17 years we burnt though more than 1.2% of the entire world’s total budget of carbon emissions. A total budget that has to last from the dawn of industrialization to the point at which the whole world become carbon-neutral. Oh, and Canada has 0.5% of the world’s population.

Disclaimer: I have to check whether the Hadley Centre’s target is 1 trillion tonnes of CO2-equivalent, or 1 trillion tonnes of Carbon (they are different!). The EnvCanada report numbers refer to the former.

Update: I checked with Chris, and as I feared, I got the wrong units – it’s a trillion tonnes of carbon. The conversion factor is about 3.66, so that gives us about 3.66 trillion tonnes of carbon dioxide to play with. [Note: Emissions targets are usually phrased in terms of “Carbon dioxide equivalent”, which is a bit hard to calculate as different greenhouse gases have both different molecular weights and different warming factors].

So my revised figures are that Canada burnt through only about 0.33% of the world’s total budget in the last 17 years. Which looks a little better, until you consider:

by population, that’s 2/3 of Canada’s entire share.

Using the cumulative totals from 1900-2002. plus the figures for the more recent years from the Environment Canada report (and assuming 2008 was similar to 2007) we’ve emitted 27 gigatonnes of CO2 since 1900. Which is about 0.73% of the world’s budget, or about 147% of our fair share per head.

By population, our fair share of the world’s budget is about 18 gigatonnes CO2 (=5 gigatonnes Carbon). We’d burnt through that by 1997. Everything since then is someone else’s share.